Field of the Disclosure
Embodiments of the present application relate to a vibration damper which is an apparatus for damping torsional vibrations of a rotary member such as a crank shaft and a power transmission shaft, and particularly to an apparatus which damps the torsional vibrations by reciprocating of inertial masses by the torsional vibrations.
Discussion of the Related Art
In JP-A-2014-504351 and PCT International publication No. 2013/118293, torsional-vibration dampers which include a rotary member having a disc shape, coupled with a rotary shaft, and inertial masses that are arcuate, provided four each in a circumferential direction on both sides of the rotary member, have been described. Each inertial mass is coupled with the rotary member to be able to undergo a pendulum movement in the circumferential direction of the rotary member. A plurality of recesses having an arcuate surface which is convex toward an outer side in a radial direction are formed at a predetermined interval in the circumferential direction. In each inertial mass, two recesses having a contact surface which is convex toward an inner side in the radial direction are arranged side-by-side in the circumferential direction. A pin is inserted through the recesses formed in the rotary member and the recesses formed in the inertial mass. The inertial mass provided to one side surface of the rotary member and the inertial mass provided to the other side surface of the rotary member are coupled, and the pendulum movement of the inertial mass is guided by the pin.
In the vibration damper described in PCT International publication No. 2013/118293, for preventing an end portion of the inertial mass from being protruded out from an outer edge of the rotary member when the inertial mass undergoes pendulum movement, a distance between centers of curvature of the contact surfaces of the recesses formed in the rotary member is larger than a distance between centers of curvature of the contact surfaces of the recesses formed in the inertial masses.
In each conventional vibration damper, an arrangement is made such that vibration of a predetermined order that has been determined in advance in design is damped. Consequently, when a torque of the rotary member changes, the plurality of inertial masses fitted to the rotary member undergo the pendulum movement in the same direction almost simultaneously. When such type of vibration damper is used to prevent the torsional vibrations of an engine in which the number of combustion cylinders can be changed, since the primary vibration mode changes in accordance with the number of combustion cylinders, an initial vibration damping performance cannot be achieved in one of the anteroposterior number of the combustion cylinders to be changed. In other words, the conventional vibration damper has no feature other than single vibration damping.
In a vibration damper that damps the vibrations of a rotary member by pendulum movement of inertial masses, a square root of ratio of a dimension from a center of rotation of the rotary member up to a center of pendulum movement of the inertial mass and a radius of pendulum movement of the inertial mass is equivalent to an order of vibration to be damped. Consequently, when the radius of pendulum movement of one of the plurality of inertial masses fitted to the rotary member is let to differ from the radius of pendulum movement of the other inertial mass, it is possible to achieve a vibration damper having a plurality of vibration damping features. However, in such vibration damper, since a cycle and a phase of vibration of each inertial mass differ when the vibration is generated in the torque of the rotary member, there is a possibility of collision of the inertial masses thereby causing noise, or degradation of vibration damping performance.